The present invention relates to cantilevered mast drilling rigs. More particularly, the present invention relates to a method and apparatus for erecting the mast and drill rig floor to their elevated operating positions over the well in a single operation.
Cantilevered mast drilling rigs are extensively used in land based drilling operations. Various approaches have been practiced by the prior art in constructing, assemblying, and erecting these cantilevered mast drilling rigs over a well site. In its operating configuration, the drilling rig is characterized by a substructure support arrangement which rests on the ground. This sub-base structure supports both the mast in its vertical operating position and the drill rig floor, which is also elevated some distance above the ground. Various items of equipment, such as an "Iron Roughneck", a rotary table, a drawworks, etc., are typically used during drilling operations on the drill rig floor in the elevated position.
In the prior art, the erection of a cantilevered mast drilling rig involved the operations of first elevating the cantilevered mast from a horizontal position at the ground level to a vertical position over the well. Secondly, a drill rig floor was then elevated from a horizontal position at the ground to the desired operating height with the rotary table positioned over the centerline of the well. In all known instances, the erection of a cantilevered mast drilling rig to its elevated operating position has involved at least a two-step operation.
Preliminary to the erection operation, the various sections of the mast, the substructure support apparatus, and the drill rig floor components are all assembled on the ground above the well site. The "fastline" from the drawworks is then reeved over the fastline sheave at the top of the mast, through the traveling block (to become the "drill lines"), and fastened to at a deadline anchor. The erection of the drilling rig then proceeds with the two-step operation.
In the first step, the cantilevered mast is rotated from its horizontal position at the ground level to its vertical operating position. The erection force is typically provided by operation of the drawworks. In most instances, the mast is pinned to a portion or what eventually will be the drill rig floor. In the second operation, the drilling rig floor with the elevated mast is then raised to the horizontal operating position above the well. The cantilevered drilling rig manufactured by Dreco incorporates a pair of A-leg assemblies at one end of the substructure support. Over these A-leg assemblies pass a series of cables. These cables provide the lifting force for raising the elevated mast and rig floor to the final elevated operating position.
The cantilevered mast drilling rig manufactured by Olympic Ironworks, Ltd., is raised in a similar two-step operation. First, the conventional mast is raised by operation of the drawworks prior to elevating of the drill floor. The entire drill floor assembly with upright mast is then raised to the operating position using substructure mounted cylinders or winches. Four support legs for the drill rig are powered during the raising operation. These legs are pinned to both the substructure support apparatus as well as the floor so that as the floor and elevated mast are raised, the floor remains horizontal at all times. U.S. Pat. Nos. 3,271,915; 3,803,780; and 4,375,241 are further example of cantilevered mast drilling rigs which are erected in two-step operations. For example, U.S. Pat. No. 3,803,780 illustrates a first step operation in which the mast is elevated by actuation of the drawworks which is positioned on the ground on top of the sub-base support structure. The second step operation utilizes the power of the drawworks to raise the drill floor containing the drawworks up to the elevated operating position. U.S. Pat. No. 4,375,241 discloses an erection technique whereby the mast is first elevated to the vertical position by the drawworks followed by a second operation in which the floorand elevated mast are raised vertically straight up to the elevated operating position. Hydraulic piston arrangements are provided for elevating the floor and mast in the second step of the erection operation.
The cantilevered mast drilling rig manufactured by Branham Industries, Inc., the "Swing Lift", likewise is erected in a two-step operation. The mast is first pinned to the substructure support. The drill floor for the Swing Lift rig is divided into two halves. On a first half, the "drawworks floor", is mounted the drawworks. The drawworks is used in the first erection step to raise the mast and the second half of the drill floor, the "setback floor", to the vertical operating position. The "sling line" from the drawworks used to erect the mast is then re-reeved onto additional sheaves on the drawworks floor, and the drawworks then used to raise that half of the drill floor up to the operating position. The cantilevered mast of the Swing Lift rig is pinned to and supported by the sub-base support structure at all times. However, enough structural height is provided to permit the drilling rig floor to be elevated to its proper height.
These two-step erection operations for erecting prior-art cantilevered mast drilling rigs have several disadvantages. First, the operation of elevating the portion of the drill rig floor containing the drawworks up to the desired elevated position requires that an operator ride the floor up to the operating position. This is dangerous, and in all cases, the two-step operation is slow and costly. In many instances, the tools needed for the drilling operations must wait until the floor has been lifted to the elevated operating position before they may be installed. This adds to the danger of the erection operation, as well as, requiring the use of expensive large cranes to lift the tools from the ground to the drill floor.